Abstract:

The present invention is a plasma etching method including: an arranging
step of arranging a pair of electrodes oppositely in a chamber and making
one of the electrodes support a substrate to be processed in such a
manner that the substrate is arranged between the electrodes, the
substrate having an organic-material film and an inorganic-material film;
and an etching step of applying a high-frequency electric power to at
least one of the electrodes to form a high-frequency electric field
between the pair of the electrodes, supplying a process gas into the
chamber to form a plasma of the process gas by means of the electric
field, and selectively plasma-etching the organic-material film of the
substrate with respect to the inorganic-material film by means of the
plasma; wherein a frequency of the high-frequency electric power applied
to the at least one of the electrodes is 50 to 150 MHz in the etching
step.

Claims:

1-26. (canceled)

27. A plasma etching unit for selectively plasma-etching an
organic-material film of a substrate having the organic-material film and
an inorganic-material thereon while using the inorganic-material film to
function as a mask, said unit comprising:a chamber configured to contain
the substrate to be processed,first and second electrodes oppositely
arranged in the chamber, the second electrode being configured to support
the substrate to be processed,a process-gas supplying system configured
to supply a process gas into the chamber,a gas-discharging system
configured to discharge a gas in the chamber, anda first high-frequency
electric power source configured to supply a high-frequency electric
power of 50 MHz to 150 MHz for forming a plasma to the second electrode,a
second high-frequency electric power source configured to apply a second
high-frequency electric power of 500 kHz to 27 MHz to the second
electrode, the second high-frequency electric power being overlapped with
the first high-frequency electric power, anda magnetic-field forming unit
configured to form a magnetic field around a plasma region between the
first and second electrodes,wherein the magnetic-field forming unit
consists of a magnetic annular unit having a plurality of rotatable,
segment magnets concentrically arranged around the chamber in such a
manner that magnetic-pole directions of adjacent two segment magnets are
opposite, and that a vertical gap is set between pair of magnets.

28. A plasma etching unit according to claim 27, whereinthe second
high-frequency electric power is 13.56 MHz.

29. A plasma etching unit according to claim 27, whereinthe second
high-frequency electric power is 3.2 MHz.

30. A plasma etching unit according to claim 27, whereina distance between
the first and second electrodes is shorter than 50 mm.

31. A plasma etching unit according to claim 27, whereina strength of the
magnetic field formed around the plasma region between the first and
second electrodes by the magnetic-field forming unit is 0.03 to 0.045 T
(300 to 450 Gauss).

32. A plasma etching unit according to claim 27, whereina focus ring is
provided around the substrate to be processed, andwhen the magnetic-field
forming unit forms a magnetic field around the plasma region between the
first and second electrodes, a strength of the magnetic field on the
focus ring is not lower than 0.001 T (10 Gauss) and a strength of the
magnetic field on the substrate to be processed is not higher than 0.001
T.

33. A plasma etching unit according to claim 27, whereinpower density of
the first high-frequency electric power is 2.12 to 4.25 W/cm.sup.2.

34. A plasma etching unit according to claim 27, whereinthe
gas-discharging system is configured to make a pressure in the chamber be
13.3 to 106.7 Pa.

35. A plasma etching unit according to claim 27, whereinthe
gas-discharging system is configured to make a pressure in the chamber be
1.33 to 6.67 Pa.

36. A plasma etching unit according to claim 27, whereina power density of
the second high-frequency electric power is not higher than 4.25
W/cm.sup.2.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to a plasma etching method of
plasma-etching an organic-material film, such as a
low-dielectric-constant film (low-k film), formed on a substrate to be
processed, such as a semiconductor wafer, by using an inorganic-material
film as a mask.

DESCRIPTION OF THE RELATED ART

[0002]In a wiring step of a semiconductor device, an interlayer dielectric
film, which has been formed between wiring layers, may be etched in order
to electrically connect the wiring layers. Recently, it has been
requested to use a film having a lower dielectric constant as the
interlayer dielectric film, in order to achieve more speeding-up of the
semiconductor device. Some organic-material films have started to be used
as such a film having a lower dielectric constant.

[0003]Etching process for the organic-material films is carried out by a
plasma etching by using an inorganic-material film such as a
silicon-oxide film as a mask. Specifically, a pair of opposite electrodes
is arranged in a chamber in such a manner that the electrodes are
vertically opposite, a semiconductor wafer (hereafter, referred to as a
mere "wafer") is placed on a lower electrode, and a high-frequency
electric power of about 13.56 to 40 MHz is supplied to the lower
electrode to carry out the etching process.

[0004]However, under a conventional etching condition, when an
organic-material film is etched by using an inorganic-material film as a
mask, in order to increase plasma density to achieve a higher etching
rate, a self-bias electric voltage has to be raised. However, if the
self-bias electric voltage is raised, an etching selective ratio of the
organic-material film with respect to the inorganic-material film as a
mask may be decreased. That is, under the conventional etching condition,
a high etching rate and a high etching selective ratio conflict with each
other.

SUMMARY OF THE INVENTION

[0005]This invention is developed by focusing the aforementioned problems
in order to resolve them effectively. An object of the present invention
is to provide a plasma etching method that can etch an organic-material
film with a high etching rate and a high etching selective ratio with
respect to an inorganic-material film, when the organic-material film is
etched by using the inorganic-material film as a mask.

[0006]According to a result of study by the inventors, in the etching
process of the organic-material film, plasma density is dominant, and ion
energy contributes only a little. On the other hand, in the etching
process of the inorganic-material film, both the plasma density and the
ion energy are necessary. Thus, in order to raise an etching rate of the
organic-material film and in order to raise an etching selective ratio of
the organic-material film with respect to the inorganic-material film,
the plasma density has to be high and the ion energy has to be low to
some extent. In the case, the ion energy of the plasma indirectly
corresponds to a self-bias electric voltage of an electrode at the
etching process. Thus, in order to etch the organic-material film with a
high etching rate and a high etching selective ratio, finally, it is
necessary to etch the organic-material film under a condition of high
plasma density and low bias. According to a further result of study by
the inventors, when the frequency of the high-frequency electric power
applied to the electrode is high, a condition wherein the plasma density
is high and the self-bias electric voltage is small can be generated.

[0007]The present invention is a plasma etching method comprising: an
arranging step of arranging a pair of electrodes oppositely in a chamber
and making one of the electrodes support a substrate to be processed in
such a manner that the substrate is arranged between the electrodes, the
substrate having an organic-material film and an inorganic-material film;
and an etching step of applying a high-frequency electric power to at
least one of the electrodes to form a high-frequency electric field
between the pair of the electrodes, supplying a process gas into the
chamber to form a plasma of the process gas by means of the electric
field, and selectively plasma-etching the organic-material film of the
substrate with respect to the inorganic-material film by means of the
plasma; wherein a frequency of the high-frequency electric power applied
to the at least one of the electrodes is 50 to 150 MHz in the etching
step.

[0008]According to the present invention, since the frequency of the
high-frequency electric power applied to the electrode is 50 to 150 MHz,
which is higher than prior art, although the plasma has high density, a
lower self-bias electric voltage can be achieved. Thus, the
organic-material film can be etched with a high etching rate and a high
etching selective ratio with respect to the inorganic-material film.

[0009]It is more preferable that the frequency of the high-frequency
electric power applied to the electrode is 70 to 100 MHz. In addition, it
is preferable that plasma density in the chamber is 5×1010 to
2×1011 cm-3, and that a self-bias electric voltage of an
electrode is not higher than 900 V.

[0010]In addition, the present invention is a plasma etching method
comprising: an arranging step of arranging a pair of electrodes
oppositely in a chamber and making one of the electrodes support a
substrate to be processed in such a manner that the substrate is arranged
between the electrodes, the substrate having an organic-material film and
an inorganic-material film; and an etching step of applying a
high-frequency electric power to at least one of the electrodes to form a
high-frequency electric field between the pair of the electrodes,
supplying a process gas into the chamber to form a plasma of the process
gas by means of the electric field, and selectively plasma-etching the
organic-material film of the substrate with respect to the
inorganic-material film by means of the plasma; wherein, in the etching
step, plasma density in the chamber is 5×1010 to
2×1011 cm-3, and a self-bias electric voltage of an
electrode is not higher than 900 V.

[0011]According to the present invention, since the plasma is generated in
a condition wherein the plasma density in the chamber is
5×1010 to 2×1011 cm-3 and wherein the
self-bias electric voltage of an electrode is not higher than 900 V, the
organic-material film can be etched with a high etching rate and a high
etching selective ratio with respect to the inorganic-material film.

[0012]It is preferable that power density of the high-frequency electric
power is 2.12 to 4.25 W/cm2.

[0013]In addition, it is preferable that a pressure in the chamber is 13.3
to 106.7 Pa or 1.33 to 6.67 Pa.

[0014]In addition, it is preferable that the high-frequency electric power
is applied to an electrode supporting the substrate to be processed. In
the case, a second high-frequency electric power of 500 kHz to 27 MHz may
be applied to the electrode supporting the substrate to be processed, the
second high-frequency electric power being overlapped with the
high-frequency electric power. By overlapping the second high-frequency
electric power of a lower frequency with the high-frequency electric
power, plasma density and ion drawing effect can be adjusted so that an
etching rate of the organic-material film can be raised more while a high
etching selective ratio with respect to the inorganic-material film can
be assured. It is preferable that a frequency of the second
high-frequency electric power is 13.56 MHz or 3.2 MHz. If the frequency
of the second high-frequency electric power is 3.2 MHz, it is preferable
that power density of the second high-frequency electric power is not
higher than 4.25 W/cm2.

[0015]In addition, the present invention is a plasma etching method
comprising: an arranging step of arranging a pair of electrodes
oppositely in a chamber and making one of the electrodes support a
substrate to be processed in such a manner that the substrate is arranged
between the electrodes, the substrate having an organic-material film and
an inorganic-material film; and an etching step of applying a
high-frequency electric power to at least one of the electrodes to form a
high-frequency electric field between the pair of the electrodes,
supplying a process gas into the chamber to form a plasma of the process
gas by means of the electric field, and selectively plasma-etching the
organic-material film of the substrate with respect to the
inorganic-material film by means of the plasma; wherein, in the etching
step: a pressure in the chamber is 13.3 to 106.7 Pa; the first
high-frequency electric power is applied to an electrode supporting the
substrate to be processed; a frequency of the first high-frequency
electric power is 50 to 150 MHz; power density of the first
high-frequency electric power is 2.12 to 4.25 W/cm2; a second
high-frequency electric power is applied to the electrode, the second
high-frequency electric power being overlapped with the first
high-frequency electric power; a frequency of the second high-frequency
electric power is 500 kHz to 27 MHz; power density of the second
high-frequency electric power is not higher than 4.25 W/cm2; plasma
density in the chamber is 5×1010 to 2×1011
cm-3; and a self-bias electric voltage of an electrode is not higher
than 900 V.

[0016]According to the above condition, vertical component of ion energy
onto the substrate to be processed can be relatively reduced, so that the
organic-material film can be etched with a high etching selective ratio
with respect to the inorganic-material film and with a high etching rate.
In particular, when a hole is etched, a very high etching rate can be
achieved while a high etching selective ratio can be maintained.

[0017]In addition, the present invention is a plasma etching method
comprising: an arranging step of arranging a pair of electrodes
oppositely in a chamber and making one of the electrodes support a
substrate to be processed in such a manner that the substrate is arranged
between the electrodes, the substrate having an organic-material film and
an inorganic-material film; and an etching step of applying a
high-frequency electric power to at least one of the electrodes to form a
high-frequency electric field between the pair of the electrodes,
supplying a process gas into the chamber to form a plasma of the process
gas by means of the electric field, and selectively plasma-etching the
organic-material film of the substrate with respect to the
inorganic-material film by means of the plasma; wherein, in the etching
step: a pressure in the chamber is 1.33 to 6.67 Pa; the first
high-frequency electric power is applied to an electrode supporting the
substrate to be processed; a frequency of the first high-frequency
electric power is 50 to 150 MHz; power density of the first
high-frequency electric power is 2.12 to 4.25 W/cm2; a second
high-frequency electric power is applied to the electrode, the second
high-frequency electric power being overlapped with the first
high-frequency electric power; a frequency of the second high-frequency
electric power is 500 kHz to 27 MHz; power density of the second
high-frequency electric power is not higher than 0.566 W/cm2; plasma
density in the chamber is 5×1010 to 2×1011
cm-3; and a self-bias electric voltage of an electrode is not higher
than 400 V.

[0018]According to the above condition, ion energy itself can be
controlled not higher than energy by which the inorganic-material film
can be spattered, so that an etching selective ratio of the
organic-material film with respect to the inorganic-material film can be
remarkably raised while a high etching rate is maintained. In addition,
surface residue is substantially not left. In addition, when the
inorganic-material film is used as a mask, a CD-shift of the mask can be
remarkably small.

[0019]In the above features, as the organic-material film, a material
including O, C and H, or another material including Si, O, C and H may be
used. As the inorganic-material film, a material comprising at least one
of a silicon oxide, a silicon nitride and a silicon oxinitride may be
used.

[0020]In addition, the present invention is a plasma etching unit
comprising: a chamber configured to contain a substrate to be processed
having an organic-material film and an inorganic-material film; a pair of
electrodes arranged in the chamber, one of the pair of electrodes being
configured to support the substrate to be processed; a process-gas
supplying system configured to supply a process gas into the chamber; a
gas-discharging system configured to discharge a gas in the chamber; and
a high-frequency electric power source configured to supply a
high-frequency electric power for forming a plasma to at least one of the
electrodes; wherein a frequency of high-frequency electric power
generated by the high-frequency electric power source is 50 to 150 MHz.

[0021]Preferably, the high-frequency electric power source is adapted to
apply the high-frequency electric power to an electrode supporting the
substrate to be processed. In the case, it is preferable that the plasma
etching unit further comprises a second high-frequency electric power
source configured to apply a second high-frequency electric power of 500
kHz to 27 MHz to the electrode supporting the substrate to be processed,
the second high-frequency electric power being overlapped with the
high-frequency electric power. It is preferable that the second
high-frequency electric power is of 13.56 MHz or 3.2 MHz.

[0022]Herein, because of the Paschen's law, an electric-discharge starting
voltage Vs takes a local minimum value (Paschen's minimum value) when a
product pd of a gas pressure p and a distance d between the electrodes
takes a certain value. The certain value of the product pd that
corresponds to the Paschen's minimum value is smaller when the frequency
of the high-frequency electric power is higher. Thus, when the frequency
of the high-frequency electric power is high, in order to decrease the
electric-discharge starting voltage Vs to facilitate and stabilize the
electric-discharge effect, the distance d between the electrodes has to
be reduced, if the gas pressure p is constant. Thus, in the present
invention, it is preferable that the distance between the electrodes is
shorter than 50 mm. In addition, when the distance between the electrodes
is shorter than 50 mm, residence time of the gas in the chamber can be
shortened. Thus, reaction products can be efficiently discharged, and
etching stop can be reduced.

[0023]In addition, it is preferable that the plasma etching unit further
comprises a magnetic-field forming unit configured to form a magnetic
field around a plasma region between the pair of electrodes.

[0024]When the frequency of the applied high-frequency electric power is
high, the etching rate may be higher in a central portion as a feeding
position compared with in a peripheral portion. However, if a magnetic
field is formed around a plasma region between the pair of electrodes,
plasma confining effect can be achieved so that the etching rate on the
substrate to be processed arranged in a processing space can be made
substantially the same between in an edge portion (peripheral portion) of
the substrate to be processed and in a central portion thereof. That is,
the etching rate can be made uniform.

[0025]It is preferable that strength of the magnetic field formed around a
plasma region between the pair of electrodes by the magnetic-field
forming unit is 0.03 to 0.045 T (300 to 450 Gauss).

[0026]In addition, it is preferable that a focus ring is provided around
the electrode supporting the substrate to be processed, and that when the
magnetic-field forming unit forms a magnetic field around a plasma region
between the pair of electrodes, strength of the magnetic field on the
focus ring is not lower than 0.001 T (10 Gauss) and strength of the
magnetic field on the substrate to be processed is not higher than 0.001
T.

[0027]When the strength of the magnetic field on the focus ring is not
lower than 0.001 T, drift movement of electrons may be generated on the
focus ring, so that the plasma density around the focus ring is raised to
make the plasma density uniform. On the other hand, when the strength of
the magnetic field on the substrate to be processed is not higher than
0.001 T, which substantially has no effect on the substrate to be
processed, charge-up damage can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic vertical sectional view showing a plasma
etching unit of an embodiment according to the present invention;

[0029]FIG. 2 is a horizontal sectional view schematically showing a
magnetic annular unit arranged around a chamber of the plasma etching
unit of FIG. 1;

[0030]FIGS. 3A to 3C are explanatory views of a change of a magnetic field
when segment magnets of the plasma etching unit of FIG. 1 are revolved;

[0031]FIG. 4 is a graph showing strengths of magnetic fields when the
segment magnets of the plasma etching unit of FIG. 1 are revolved;

[0032]FIG. 5 is a view showing another example of revolving operation of
segment magnets of the plasma etching unit of FIG. 1;

[0033]FIG. 6 is a view showing further another example of revolving
operation of segment magnets of the plasma etching unit of FIG. 1;

[0034]FIG. 7 is a view showing another example of segment magnets for the
plasma etching unit of FIG. 1;

[0035]FIGS. 8A to 8E are schematic views showing various arrangement
examples of the segment magnets of the plasma etching unit of FIG. 1;

[0036]FIGS. 9A and 9B are sectional views showing a structural example of
wafer to which a plasma etching process according to the present
invention is applied;

[0037]FIG. 10 is a schematic sectional view partly showing a plasma
processing unit comprising a high-frequency electric power source for
generating plasma and a high-frequency electric power source for drawing
ions;

[0038]FIG. 11 is a graph showing relationships between a self-bias
electric voltage Vdc and plasma density Ne, in respective cases wherein
the frequency of the high-frequency electric power is 40 MHz or 100 MHz,
when the plasma consists of argon gas;

[0039]FIG. 12 is a graph comparatively showing relationships between a
self-bias electric voltage and plasma density, in respective cases
wherein the plasma is formed by an Ar gas or an etching gas, when the
frequency of the high-frequency electric power is 100 MHz;

[0040]FIG. 13A is a graph showing etching rates of an organic-material
film at a wafer position, in samples of respective cases wherein the
high-frequency electric power is 500 W, 1000 W or 1500 W, when the
frequency of the high-frequency electric power is 100 MHz;

[0041]FIG. 13B is a graph showing etching rates of an organic-material
film at a wafer position, in samples of respective cases wherein the
high-frequency electric power is 500 W, 1000 W or 1500 W, when the
frequency of the high-frequency electric power is 40 MHz;

[0042]FIG. 14 is a graph showing relationships between a high-frequency
electric power and an etching rate of the organic-material film, in
samples of respective cases wherein the frequency of the high-frequency
electric power is 40 MHz or 100 MHz;

[0043]FIG. 15 is a graph showing relationships between a high-frequency
electric power and an etching rate of the inorganic-material film, in
samples of respective cases wherein the frequency of the high-frequency
electric power is 40 MHz or 100 MHz;

[0044]FIG. 16 is a graph showing relationships between an etching rate of
the organic-material film and a ratio (an etching rate of the
organic-material film/an etching rate of the inorganic-material film)
corresponding to an etching selective ratio, in samples of respective
cases wherein the frequency of the high-frequency electric power is 40
MHz or 100 MHz;

[0045]FIG. 17 is a graph showing relationships between a high-frequency
electric power and an etching rate of the organic-material film and
relationships between a high-frequency electric power and an etched
volume of a shoulder part of the inorganic-material film (shoulder loss),
wherein the real pattern shown in FIG. 9 is used;

[0046]FIG. 18 is a graph showing relationships between an etching rate of
the organic-material film and an etching selective ratio with respect to
an etching rate of the shoulder part of the inorganic-material film, in
respective cases wherein the frequency of the high-frequency electric
power is 40 MHz or 100 MHz, wherein the real pattern shown in FIG. 9 is
used;

[0047]FIG. 19 is a view for explaining a shoulder loss;

[0048]FIG. 20 is a graph comparatively showing relationships between an
Ar-gas flow rate and a pressure difference ΔP of a central portion
of the wafer and a peripheral portion thereof, in respective cases
wherein an electrode gap is 25 mm or 40 mm, wherein the Ar gas is used as
a plasma gas;

[0049]FIG. 21 is a graph showing relationships between the electric power
of 3.2 MHz and an etching rate of the organic-material film and
relationships between the electric power of 3.2 MHz and an etching
selective ratio with respect to the shoulder part, in respective pressure
conditions;

[0050]FIG. 22 is a graph showing relationships between the electric power
of 3.2 MHz and a top CD shift, in respective pressure conditions;

[0051]FIG. 23 is a graph showing relationships between the electric power
of 3.2 MHz and a bowing value, in respective pressure conditions;

[0052]FIG. 24 is a view for explaining a top CD shift;

[0053]FIG. 25 is a view for explaining a bowing value;

[0054]FIG. 26 is a graph showing etching residues, shoulder losses of the
inorganic-material film (mask) and top CD shifts, in respective pressure
conditions, when the bias power is zero; and

[0055]FIG. 27 is a graph showing shoulder losses of the inorganic-material
film (mask), top CD shifts and etching rates of the organic-material
film, in respective bias-power conditions, when the pressure is 3.99 Pa.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0056]An embodiment of the invention will now be described with reference
to the attached drawings.

[0057]FIG. 1 is a schematic sectional view showing a plasma etching unit
used for carrying out the present invention. The etching unit of the
embodiment includes a two-stage cylindrical chamber vessel 1, which has
an upper portion 1a having a small diameter and an lower portion 1b
having a large diameter. The chamber vessel 1 may be hermetically made of
any material, for example aluminum.

[0058]A supporting table 2 is arranged in the chamber vessel 1 for
horizontally supporting a wafer W as a substrate to be processed. The
supporting table 2 may be made of any material, for example aluminum. The
supporting table 2 is placed on a conductive supporting stage 4 via an
insulation plate 3. A focus ring 5 is arranged on a peripheral area of
the supporting table 2. The focus ring 5 may be made of any conductive
material or any insulating material. When the diameter of the wafer W is
200 mmφ, it is preferable that the focus ring 5 is 240 to 280
mmφ. The supporting table 2, the insulation plate 3, the supporting
stage 4 and the focus ring 5 can be elevated by a ball-screw mechanism
including a ball-screw 7. A driving portion for the elevation is arranged
below the supporting stage 4 and is covered by a bellows 8. The bellows 8
may be made of any material, for example stainless steel (SUS). The
chamber vessel 1 is earthed. A coolant passage (not shown) is formed in
the supporting table 2 in order to cool the supporting table 2. A bellows
cover 9 is provided around the bellows 8.

[0059]A feeding cable 12 for supplying a high-frequency electric power is
connected to a substantially central portion of the supporting table 2.
The feeding cable 12 is connected to a high-frequency electric power
source 10 via a matching box 11. A high-frequency electric power of a
predetermined frequency is adapted to be supplied from the high-frequency
electric power source 10 to the supporting table 2. A showerhead 16 is
provided above the supporting table 2 and oppositely in parallel with the
supporting table 2. The showerhead 16 is also earthed. Thus, the
supporting table 2 functions as a lower electrode, and the showerhead 16
functions as an upper electrode. That is, the supporting table 2 and the
showerhead 16 form a pair of plate electrodes.

[0060]Herein, it is preferable that the distance between the electrodes is
set to be shorter than 50 mm. The reason is as follows.

[0061]Because of the Paschen's law, an electric-discharge starting voltage
Vs takes a local minimum value (Paschen's minimum value) when a product
pd of a gas pressure L and a distance d between the electrodes takes a
certain value. The certain value of the product pd that corresponds to
the Paschen's minimum value is smaller when the frequency of the
high-frequency electric power is higher. Thus, when the frequency of the
high-frequency electric power is high like the present embodiment, in
order to decrease the electric-discharge starting voltage Vs to
facilitate and stabilize the electric-discharge effect, the distance d
between the electrodes has to be reduced, if the gas pressure L is
constant. Thus, it is preferable that the distance between the electrodes
is shorter than 50 mm. In addition, when the distance between the
electrodes is shorter than 50 mm, residence time of the gas in the
chamber can be shortened. Thus, reaction products can be efficiently
discharged, and etching stop can be reduced.

[0062]However, if the distance between the electrodes is too short,
pressure distribution on the surface of the wafer W as a substrate to be
processed (pressure difference between in a central portion and in a
peripheral portion) may become large. In the case, problems such as
deterioration of etching uniformity may be generated. Independently on
gas flow rate, in order to make the pressure difference smaller than 0.27
Pa (2 mTorr), it is preferable that the distance between the electrodes
is not shorter than 35 mm.

[0063]An electrostatic chuck 6 is provided on an upper surface of the
supporting table 2 in order to electrostaticly stick to the wafer W. The
electrostatic chuck 6 consists of an insulation plate 6b and an electrode
6a inserted in the insulation plate 6b. The electrode 6a is connected to
a direct-current power source 13. Thus, when the power source 13 supplies
an electric power to the electrode 6a, the semiconductor wafer W may be
stuck to the electrostatic chuck 6 by coulomb force, for example.

[0064]The coolant passage not shown is formed in the supporting table 2.
The wafer W can be controlled at a predetermined temperature by
circulating a suitable coolant in the coolant passage. In order to
efficiently transmit heat of cooling from the suitable coolant to the
wafer W, a gas-introducing mechanism (not shown) for supplying a He gas
onto a reverse surface of the wafer W is provided. In addition, a baffle
plate 14 is provided at an outside area of the focus ring 5. The baffle
plate 14 is electrically connected to the chamber vessel 1 via the
supporting stage 4 and the bellows 8.

[0065]The showerhead 16 facing the supporting table 2 is provided in a
ceiling of the chamber vessel 1. The showerhead 16 has a large number of
gas jetting holes 18 at a lower surface thereof and a gas introducing
portion 16a at an upper portion thereof. Then, an inside space 17 is
formed between the gas introducing portion 16a and the large number of
gas jetting holes 18. The gas introducing portion 16a is connected to a
gas supplying pipe 15a. The gas supplying pipe 15a is connected to a
process-gas supplying system 15, which can supply a process gas for
etching. As the process gas for etching, at least one of an N2 gas,
an H2 gas, an O2 gas, a CO gas, an NH3 gas, a
CxHy gas (x and y are natural numbers) and a rare gas such as
Ar or He may be used. For example, a mixed gas of an N2 gas and an
O2 gas, or a mixed gas of an N2 gas and an H2 gas may be
used.

[0066]The process gas is supplied from the process-gas supplying system 15
into the space 17 of the showerhead 16 through the gas supplying pipe 15a
and the gas introducing portion 16a. Then, the process gas is jetted from
the gas jetting holes 18 in order to etch a film formed on the wafer W.

[0067]A discharging port 19 is formed at a part of a side wall of the
lower portion 1b of the chamber 1. The discharging port 19 is connected
to a gas-discharging system 20 including a vacuum pump. A pressure of an
inside of the chamber vessel 1 may be reduced to a predetermined vacuum
level by operating the vacuum pump. A transferring port for the wafer W
and a gate valve 24 for opening and closing the transferring port are
arranged at another upper part of the side wall of the lower portion 1b
of the chamber vessel 1.

[0068]A magnetic annular unit 21 is concentrically arranged around the
upper portion 1a of the chamber vessel 1. Thus, a magnetic field may be
formed around a processing space between the supporting table 2 and the
showerhead 16. The magnetic annular unit 21 may be caused to revolve
around a center axis thereof (along an annular peripheral edge thereof)
by a revolving mechanism 25.

[0069]The magnetic annular unit 21 has a plurality of segment magnets 22
which are supported by a holder not shown and which are arranged
annularly. Each of the plurality of segment magnets 22 consists of a
permanent magnet. In the embodiment, 16 segment magnets 22 are arranged
annularly (concentrically) in a multi-pole state. That is, in the
magnetic annular unit 21, adjacent two segment magnets 22 are arranged in
such a manner that their magnetic-pole directions are opposite. Thus, a
magnetic line of force is formed between the adjacent two segment magnets
22 as shown in FIG. 2, so that a magnetic field of 0.02 to 0.2 T (200 to
2000 Gauss), preferably 0.03 to 0.045 T (300 to 450 Gauss), is generated
only around the processing space. On the other hand, in a region wherein
the wafer is placed, a substantially non-magnetic field state is
generated. The above strength of the magnetic field is determined because
of the following reasons: if the magnetic field is too strong, a fringing
field may be caused; and if the magnetic field is too weak, plasma
confining effect can not be achieved. Of course, the suitable strength of
the magnetic field also depends on the unit structure or the like. That
is, the range of the suitable strength of the magnetic field may be
different for respective units.

[0070]When the above magnetic field is formed around the processing space,
strength of the magnetic field on the focus ring 5 is desirably not lower
than 0.001 T (10 Gauss). In the case, drift movement of electrons
(E×B drift) is generated on the focus ring, so that the plasma
density around the wafer is increased, and hence the plasma density is
made uniform. On the other hand, in view of preventing charge-up damage
of the wafer W, strength of the magnetic field in a portion where the
wafer W is positioned is desirably not higher than 0.001 T (10 Gauss).

[0071]Herein, the substantially non-magnetic state in a region occupied by
the wafer means a state that there is not a magnetic field affecting the
etching process in the area occupied by the wafer. That is, the
substantially non-magnetic state includes a state that there is a
magnetic field not substantially affecting the wafer process.

[0072]In the state shown in FIG. 2, a magnetic field whose density is not
more than 420 μT (4.2 Gauss) is applied to a peripheral area of the
wafer. Thus, plasma confining function can be achieved.

[0073]When a magnetic field is formed by the magnetic annular unit of the
multi-pole state, wall portions of the chamber 1 corresponding to the
magnetic poles (for example, portions shown by P in FIG. 2) may be
locally whittled. Thus, the magnetic annular unit 21 may be caused to
revolve along the peripheral direction of the chamber by the above
revolving mechanism 25. Thus, it is avoided that the magnetic poles are
locally abutted (located) against the chamber wall, so that it is
prevented that the chamber wall is locally whittled.

[0074]Each segment magnet 22 is configured to freely revolve around a
perpendicular axis thereof by a segment-magnet revolving mechanism not
shown. That is, from a state shown in FIGS. 2 and 3A wherein the magnetic
poles of the segment magnets 22 are oriented toward the chamber 1,
adjacent two segment magnets 22 revolve synchronously and oppositely
through a state shown in FIG. 3B to a state shown in FIG. 3C (every other
segment magnet 22 revolves in the same direction). Herein, FIG. 3B shows
a state wherein the segment magnets 22 have revolved by 45 degrees, and
FIG. 3C shows a state wherein the segment magnets 22 have revolved by 90
degrees.

[0075]FIG. 4 is a graph showing relationships between a distance from the
center of the wafer W and strength of the magnetic field, in a case shown
in FIG. 3A (curve A), in a case shown in FIG. 3B (curve B) and in a case
shown in FIG. 3C (curve C). The transverse axis represents the distance
from the center of the wafer W placed on the supporting table 2 in the
chamber 1, and the ordinate axis represents the strength of the magnetic
field. In the state shown in FIG. 3A, as shown by the curve A, a
multi-pole magnetic field is formed substantially to a peripheral portion
of the wafer W. On the other hand, in the state shown in FIG. 3C, as
shown by the curve C, there is formed substantially no magnetic field in
the chamber 1. The state shown in FIG. 3B is a magnetic-field state
between them.

[0076]That is, when the segment magnets 22 are caused to revolve as shown
in FIGS. 3A to 3C, the state wherein the multi-pole magnetic field is
substantially formed and the state wherein the multi-pole magnetic field
is not formed can be switched. Depending on a kind of film to be etched,
the multi-pole magnetic field may be effective or not. Thus, when the
state wherein the multi-pole magnetic field is formed and the state
wherein the multi-pole magnetic field is not formed can be switched, a
suitable etching condition can be selected correspondingly to the film.

[0077]The revolving manner of the segment magnets 22, for switching
between the state wherein the multi-pole magnetic field is formed and the
state wherein the multi-pole magnetic field is not formed, is not limited
to the manner shown in FIG. 3. For example, as shown in FIG. 5, all the
segment magnets 22 may be configured to revolve in the same direction.
Alternatively, as shown in FIG. 6, only every other segment magnet 22 may
be configured to revolve while the other segment magnets 22 may be fixed.
When the manner shown in FIG. 6 is adopted, the number of revolving
segment magnets 22 is reduced, so that the revolving mechanism may be
made simpler. In addition, as shown in FIG. 7, one magnetic pole may
consist of a set of a plurality of segment magnets, for example a set of
three segment magnets 22a, 22b and 22c. In the case, these segment
magnets 22a, 22b and 22c may synchronously revolve in the same direction.
Like this, if a larger number of segment magnets are used, the strength
of the magnetic field can be enhanced more.

[0079]FIGS. 8A to 8E are schematic views showing various arrangement
examples of the segment magnets.

[0080]FIG. 8A is a standard arrangement example. In the case, the segment
magnets 22 are arranged away from a lateral wall of the chamber 1 by a
predetermined distance m. A profile of magnetic field generated by this
arrangement may be adjusted by changing magnetic forces and/or vertical
lengths of the segment magnets 22.

[0081]In examples shown in FIGS. 8B and 8C, each segment magnet 22 is
vertically bisected into a magnet 22d and a magnet 22e. Then, a set of
annularly arranged magnets 22d and a set of annularly arranged magnets
22e are respectively vertically movable. As shown in FIG. 8B, when a gap
between the magnets 22d and 22e is small and a distance between the
magnets and a wafer edge is short, a relatively large magnetic field is
formed in a periphery of the edge of the wafer W. On the other hand, as
shown in FIG. 8C, when a gap between the magnets 22d and 22e is large and
a distance between the magnets and a wafer edge is long, a relatively
small magnetic field is formed in a periphery of the edge of the wafer W.
Herein, the divided magnets 22d and 22e may have the same magnetization
direction. However, it is more preferable that they have opposite
magnetization directions, because the same magnetic-pole portions (P
portions shown in FIG. 2) are dispersed so that whittling of the
inner-wall portion of the chamber 1 is prevented.

[0082]In examples shown in FIGS. 8D and 8E, a set of the divided magnets
22d and a set of the divided magnets 22e are respectively forward and
backward movable. As shown in FIG. 8D, when the magnets 22d and 22e are
located nearer to the lateral wall of the chamber 1 than the
predetermined distance m (when the diameters of the annular magnetic
units respectively formed by the magnets 22d and 22e are small), a
stronger magnetic field is formed around the processing space. On the
other hand, as shown in FIG. 8E, when the magnets 22d and 22e are located
further than the predetermined distance m (when the diameters of the
annular magnetic units are large), a weaker magnetic field is formed
around the processing space.

[0083]As described above, by variously changing the arrangement of the
segment magnets, various profiles of magnetic field can be formed. Thus,
it is preferable to arrange the segment magnets so as to obtain a
required profile of magnetic field.

[0084]The number of the segment magnets is not limited to the above
examples. The section of each segment magnet is not limited to the
rectangle, but may have any shape such as a circle, a square, a trapezoid
or the like. A magnetic material forming the segment magnets 22 is also
not limited, but may be any known magnetic material such as a rare-earth
magnetic material, ferrite magnetic material, an Arnico magnetic
material, or the like.

[0085]Next, an operation for etching a low-dielectric-constant film (low-k
film) as an organic-material film by using the above plasma etching unit
and by using an inorganic-material film as a mask is explained.

[0086]In a wafer W before being etched, as shown in FIG. 9A, an
organic-material film 42 that is a low-k film is formed as an interlayer
dielectric film on a silicon substrate 41. Then, an inorganic-material
film 43 having a predetermined pattern is formed as a hard mask on the
organic-material film 42. Thereon, a BARC layer 44 is formed. Then, a
resist film 45 having a predetermined pattern is formed thereon.

[0087]The inorganic-material film 43 consists of a material generally used
as a hard mask. As a suitable example, it may be a silicon oxide, a
silicon nitride, a silicon oxinitride, or the like. That is, it is
preferable that the inorganic-material film 43 consists of at least one
of the above materials.

[0088]The organic-material film 42 to be etched is a low-k film used as an
interlayer dielectric film, as described above. Thus, the dielectric
constant of the organic-material film 42 is much smaller than that of a
silicon oxide which is a conventional material for an interlayer
dielectric film. The low-k film of the organic-material consists of, for
example, a polyorganosiloxane-bridge bisbenzocyclobutene resin (BCB), a
polyaryleneether resin (PAE) such as SiLK (commercial name) and FLARE
(commercial name) made by DowChemical Company, an organic polysiloxane
resin such as methylsilsesquioxane (MSQ), or the like. Herein, the
organic polysiloxane means a material having a structure wherein a
functional group including C, H is included in a bonding-structure of a
silicon oxide film, as shown below. In the structure shown below, R means
an alkyl group such as a methyl group, an ethyl group, a propyl group or
the like; or a derivative thereof; or an aryl group such as a phenyl
group: or a derivative thereof.

##STR00001##

[0089]In the wafer W of the above structure, the BARC layer 44 and the
inorganic-material film 43 are etched while the resist film 45 is used as
a mask. The state is shown in FIG. 9B. In the step, the thickness of the
resist film 45 is reduced by the etching.

[0090]Then, the organic-material film 42 is etched while the resist film
45 and the inorganic-material film 43 are used as a mask. At first, the
gate valve 24 of the unit of FIG. 1 is opened, a wafer W of the structure
shown in FIG. 9B is conveyed into the chamber 1 by means of a conveying
arm, and placed on the supporting table 2. After that, the conveying arm
is evacuated, the gate valve 24 is closed, and the supporting table 2 is
moved up to a position shown in FIG. 1. The vacuum pump of the
gas-discharging system 20 creates a predetermined vacuum in the chamber 1
through the discharging port 19.

[0091]Then, a predetermined process gas, for example an N2 gas and an
O2 gas, is introduced into the chamber 1 through the process-gas
supplying system 15, for example at a flow rate of 0.1 to 1 L/min (100 to
1000 scam). Thus, a pressure in the chamber 1 is maintained at a
predetermined pressure, for example about 1.33 to 133.3 Pa (10 to 1000
mTorr). Within the pressure range, in order to maintain a high etching
selective ratio with respect to the inorganic-material film and to etch
the organic-material film with a high etching rate, a relatively high
pressure of 13.3 to 106.7 Pa (100 to 800 mTorr) is preferable. On the
other hand, in order to achieve an etching process wherein an etching
selective ratio with respect to the inorganic-material film is very high,
residue is less, and accuracy of form is good, a relatively low pressure
of 1.33 to 6.67 Pa (10 to 50 mTorr) is preferable. While the pressure in
the chamber 1 is maintained within such a predetermined pressure range, a
high-frequency electric power whose frequency is 50 to 150 MHz,
preferably 70 to 100 MHz, is supplied from the high-frequency electric
power source 10 to the supporting table 2. In this case, power per unit
area (hereinafter, referred to as power density) is preferably within a
range of about 1.0 to about 5.0 W/cm2. In particular, a range of
2.12 to 4.25 W/cm2 is preferable. Then, a predetermined electric
voltage is applied from the direct current power source 13 to the
electrode 6a of the electrostatic chuck 6, so that the wafer W sticks to
the electrostatic chuck 6 by means of Coulomb force, for example.

[0092]When the high-frequency electric power is applied to the supporting
table 2 as the lower electrode as described above, a high-frequency
electric field is formed in the processing space between the showerhead
16 as the upper electrode and the supporting table 2 as the lower
electrode. Thus, the process gas supplied into the processing space is
made plasma, which etches the organic-material film 42. During the
etching step, the resist film 45 functions as a mask partway. However,
during the etching step, the resist film 45 and the BARC film 44 are
etched to disappear. After that, only the inorganic-material film 43
functions as a mask, and the etching process of the organic-material film
42 is continued.

[0093]During the etching step, by means of the annular magnetic unit 21 of
a multi-pole state, a magnetic field as shown in FIG. 2 can be formed
around the processing space. In the case, plasma confining effect is
achieved, so that an etching rate of the wafer W may be made uniform,
even in a case of a high frequency like this embodiment wherein the
plasma tends to be not uniform. However, depending on the kind of the
film, the magnetic field may not have an effect. In the case, the segment
magnets may be caused to revolve in order to conduct the etching process
under a condition wherein a magnetic field is substantially not formed
around the processing space.

[0094]When the above magnetic field is formed, by means of the
electrically conductive or insulating focus ring 5 provided around the
wafer W on the supporting table 2, the effect of making the plasma
process uniform can be more enhanced. That is, if the focus ring 5
consists of an electrically conductive material such as silicon or SiC,
even a focus-ring region functions as the lower electrode. Thus, a
plasma-forming region is expanded over the focus ring 5, the plasma
process around the wafer W is promoted, so that uniformity of the etching
rate is improved. In addition, if the focus ring 5 consists of an
electrically insulating material such as quartz, electric charges can not
be transferred between the focus ring 5 and electrons and ions in the
plasma. Thus, the plasma confining effect may be increased so that
uniformity of the etching rate is improved.

[0095]In order to adjust plasma density and ion-drawing effect, the
high-frequency electric power for generating plasma and a second
high-frequency electric power for drawing ions may be overlapped with
each other. Specifically, as shown in FIG. 10, in addition to the
high-frequency electric power source 10 for generating plasma, a second
high-frequency electric power source 26 for drawing ions is connected to
the matching box 11, so that they are overlapped. In the case, the
frequency of the second high-frequency electric power source 26 for
drawing ions is preferably 3.2 to 13.56 MHz, in particular 13.56 MHz.
Thus, the number of parameters for controlling ion energy is increased so
that an optimum processing condition can be easily set wherein an etching
rate of the organic-material film is raised more while a necessary and
sufficient etching selective ratio with respect to the inorganic-material
film is assured.

[0096]Herein, according to a result of study by the inventors, in the
etching process of the organic-material film, the plasma density is
dominant, and the ion energy contributes only a little. On the other
hand, in the etching process of the inorganic-material film, both the
plasma density and the ion energy are necessary. Thus, when the
organic-material film 42 is etched by using the inorganic-material film
43 as a mask, in order to etch the organic-material film 42 with a high
etching rate and a high etching selective ratio with respect to the
inorganic-material film 43, the plasma density has to be high and the ion
energy has to be low. That is, if the ion energy necessary for etching
the inorganic-material film is low and the plasma density dominant for
etching the organic-material film is high, only the organic-material film
can be selectively etched with a high etching rate. Herein, the ion
energy of the plasma indirectly corresponds to a self-bias electric
voltage of an electrode at the etching process. Thus, in order to etch
the organic-material film with a high etching rate and a high etching
selective ratio, finally, it is necessary to etch the organic-material
film under a condition of high plasma density and low self-bias electric
voltage.

[0097]This is explained with reference to FIG. 11 as follows. FIG. 11 is a
graph showing relationships between a self-bias electric voltage Vdc and
plasma density Ne, in respective cases wherein the frequency of the
high-frequency electric power is 40 MHz or 100 MHz. The transverse axis
represents the self-bias electric voltage Vdc, and the ordinate axis
represents the plasma density. In the case, as the plasma gas, Ar was
used for evaluation, instead of real etching gas. For each frequency,
applied high-frequency electric power was changed, so that values of the
plasma density Ne and the self-bias electric voltage Vdc were changed.
That is, in the respective frequencies, if the applied high-frequency
electric power is large, both the plasma density Ne and the self-bias
electric voltage Vdc are large. Herein, the plasma density was measured
by means of a microwave interferometer.

[0098]As shown in FIG. 11, in the case wherein the frequency of the
high-frequency electric power is conventionally 40 MHz, when the plasma
density is increased to enhance the etching rate of the organic-material
film, the self-bias electric voltage Vdc is greatly increased. On the
other hand, in the case wherein the frequency of the high-frequency
electric power is 100 MHz that is higher than prior art, even when the
plasma density is increased, the self-bias electric voltage Vdc is not so
increased and controlled substantially not higher than 100 V. That is, it
was found that a condition of high plasma density and low self-bias
electric voltage can be achieved. That is, if the frequency is relatively
low like a conventional art, when the etching rate of the
organic-material film is increased in a real etching process, the
inorganic-material film is also etched to the same extent and good
selective-etching performance is not achieved. On the other hand, if the
frequency is as high as 100 MHz, it was found that the organic-material
film can be etched with a high etching rate and a high etching selective
ratio with respect to the inorganic-material film.

[0099]In addition, as seen from FIG. 11, in order to etch the
organic-material film with a high etching rate and a high etching
selective ratio by higher plasma density and lower self-bias electric
voltage than prior art, when the plasma of Ar gas is formed, it may be
thought preferable to form the plasma under a condition wherein the
plasma density is not less than 1×1011 cm-3 and the
self-bias electric voltage of the electrode is not higher than 300 V.
More preferably, the plasma density is not less than 1.5×1011
cm-3 and the self-bias electric voltage of the electrode is not
higher than 100 V. Then, in order to satisfy such a plasma condition, it
may be estimated that the frequency of the high-frequency electric power
has to be 50 MHz or higher.

[0100]Thus, the frequency of the high-frequency electric power for
generating plasma is set not less than 50 MHz, as described above.
However, if the frequency of the high-frequency electric power for
generating plasma is higher than 150 MHz, the uniformity of the plasma
may be deteriorated. Thus, it is preferable that the frequency of the
high-frequency electric power for generating plasma is not higher than
150 MHz. In particular, in order to effectively achieve the above effect,
it is preferable that the frequency of the high-frequency electric power
for generating plasma is 70 to 100 MHz.

[0101]Next, a measurement result of self-bias electric voltage and plasma
density is explained wherein a real etching gas (N2+H2) is used
and a high-frequency electric power of 100 MHz is applied. FIG. 12 is a
graph comparatively showing relationships between a self-bias electric
voltage and plasma density, in respective cases wherein the plasma is
formed by an Ar gas or an etching gas, when the frequency of the
high-frequency electric power is 100 MHz. The transverse axis represents
the self-bias electric voltage Vdc, and the ordinate axis represents the
plasma density. At that time, the pressure in the chamber was 13.3 Pa
(100 mTorr). Herein, the power of the high-frequency electric power of
100 MHz was changed, so that the plasma density and the self-bias
electric voltage Vdc were changed. In addition, the power of the
high-frequency electric power of 100 MHz was fixed to 2500 W while a
second high-frequency electric power of 3.2 MHz was overlapped in a range
of 200 to 3000 W.

[0102]As shown in FIG. 12, in the case of the plasma of real etching gas,
compared with the plasma of Ar gas, the plasma density tends to be a
little lower. In addition, when the second high-frequency electric power
of the lower frequency (3.2 MHz) is overlapped and the power is
increased, the self-bias electric voltage tends to be increased.

[0103]As described above, in the case of the high frequency of 100 MHz,
the plasma density tends to be higher and the self-bias electric voltage
tends to be lower than the conventional art. Thus, in FIG. 12, in a
condition wherein the plasma density of the etching gas at 1000 W is not
less than 5×1010 cm-3, which corresponds to
1×1011 cm-3 of the Ar plasma, the etching process can be
conducted with a high etching rate while satisfying an etching selective
ratio with respect to the inorganic-material film.

[0104]When the second high-frequency electric power of 3.2 MHz is not
overlapped, at 2800 W, the plasma density becomes 1×1011
cm-3 and the self-bias electric voltage becomes about 200 V. On the
other hand, when the second high-frequency electric power of 3.2 MHz is
overlapped and the power is increased, at 3000 W, the plasma density
becomes about 1×1011 to 2×1011 cm-3 and the
self-bias electric voltage becomes about 800 to 900 V. When the
overlapped power of 3.2 MHz is increased, it is thought that the etching
rate is also increased. On the other hand, when the self-bias electric
voltage is increased, the etching selective ratio with respect to the
inorganic-material film tends to be lowered. However, until the self-bias
electric voltage reaches about 900 V, the etching selective ratio can be
maintained in an allowable range. Thus, when the overlapped power (bias
power) of the second high-frequency electric power is increased, the
etching rate may be enhanced while an etching selective ratio of a
desirable level is maintained. That is, under a condition wherein the
plasma density is 5×1010 to 2×1011 cm-3 and
the self-bias electric voltage of the electrode is not higher than 900 V,
it is possible that the etching process is conducted with a high etching
rate while maintaining the etching selective ratio with respect to the
inorganic-material film within a desirable range.

[0105]Next, specific preferable conditions are explained.

[0106]At first, they includes a condition wherein: a pressure in the
chamber 1 is 13.3 to 106.7 pa (100 to 800 mTorr) that is high; a first
high-frequency electric power having a frequency of 50 to 150 MHz, for
example 100 MHz, and a power density of 2.12 to 4.25 W/cm2 is
applied to the supporting table 2; if necessary, a second high-frequency
electric power having a frequency of 500 kHz to 27 MHz, for example 3.2
MHz, and a power density of not higher than 4.25 W/cm2 is applied to
be overlapped with the first high-frequency electric power; the plasma
density is 5×1010 to 2×1011 cm-3; and the
self-bias electric voltage Vdc of the supporting table 2 as the lower
electrode is not higher than 900 V. Under the condition, since the
pressure in the chamber 1 is relatively high, vertical component of ion
energy can be relatively reduced. In addition, the bias power is adjusted
so that the organic-material film can be etched with a high etching
selective ratio with respect to the inorganic-material film and with a
high etching rate. In particular, when a hole is etched, a very high
etching rate can be achieved while a high etching selective ratio can be
maintained.

[0107]In addition, they includes a condition wherein: a pressure in the
chamber 1 is 1.33 to 6.67 pa (10 to 50 mTorr) that is low; a first
high-frequency electric power having a frequency of 50 to 150 MHz, for
example 100 MHz, and a power density of 2.12 to 4.25 W/cm2 is
applied to the supporting table 2; if necessary, a second high-frequency
electric power having a frequency of 500 kHz to 27 MHz, for example 3.2
MHz, and a power density of not higher than 0.566 W/cm2 is applied
to be overlapped with the first high-frequency electric power; the plasma
density is 5×1010 to 2×1011 cm-3; and the
self-bias electric voltage Vdc of the supporting table 2 as the lower
electrode is not higher than 400 V. Under the condition, since the
pressure in the chamber 1 is low, ion energy itself can be controlled not
higher than energy by which the inorganic-material film can be spattered.
In addition, through adjustment of the bias power or the like, the
self-bias electric voltage is limited within the relatively low range.
Thus, the organic-material film can be etched with a high etching rate
and a very high etching selective ratio with respect to the
inorganic-material film. In addition, surface residue is substantially
not left. In addition, a CD-shift of the mask of the inorganic-material
film can be remarkably reduced.

[0108]Next, in order to obtain a real etching rate of an organic-material
film and an etching selective ratio with respect to an inorganic-material
film, etching experiments for whole-surface formed films of an
organic-material film (resist) and an inorganic-material film (SiO2)
were conducted. The result is explained. Herein, a 200 mm wafer is used
as the wafer W, an N2 gas: 0.1 L/min and an O2 gas: 0.01 L/min
were supplied as an etching gas, the gap between the electrodes was 27
mm, and the pressure in the chamber was 2.66 Pa.

[0109]FIG. 13A is a graph showing etching rates of an organic-material
film at a wafer position, in respective cases wherein the high-frequency
electric power is 500 W (1.59 W/cm2), 1000 W (3.18 W/cm2) or
1500 W (4.77 W/cm2), when the frequency of the high-frequency
electric power is 100 MHz. FIG. 13B is a graph showing etching rates of
an organic-material film at a wafer position, in respective cases wherein
the high-frequency electric power is 500 W (1.59 W/cm2), 1000 W
(3.18 W/cm2) or 1500 W (4.77 W/cm2), when the frequency of the
high-frequency electric power is 40 MHz. FIG. 14 is a graph showing
relationships between a high-frequency electric power and an etching rate
of the organic-material film, in respective cases wherein the frequency
of the high-frequency electric power is 40 MHz or 100 MHz. FIG. 15 is a
graph showing relationships between a high-frequency electric power and
an etching rate of the inorganic-material film, in respective cases
wherein the frequency of the high-frequency electric power is 40 MHz or
100 MHz. FIG. 16 is a graph showing relationships between an etching rate
of the organic-material film and a ratio (an etching rate of the
organic-material film/an etching rate of the inorganic-material film)
corresponding to an etching selective ratio, in respective cases wherein
the frequency of the high-frequency electric power is 40 MHz or 100 MHz.

[0110]From these drawings, it can be seen that the etching rate of the
organic-material film is higher in the case of 100 MHz, for every power.
When the high-frequency electric power is increased, the etching rate of
the inorganic-material film tends to be increased. However, the
difference between the etching rate in the case of 40 MHz and the etching
rate in the case of 100 MHz is not large. In addition, when the
high-frequency electric power is higher, the etching rate of the
organic-material film is higher, and when the high-frequency electric
power is lower, the value corresponding to the etching selective ratio
with respect to the inorganic-material film tends to be higher. In
addition, comparing the etching rate in the case of 40 MHz and the
etching rate in the case of 100 MHz, when the value corresponding to the
etching selective ratio is the same, the etching rate in the case of 100
MHz is higher. Comparing them at the same etching rate, the value
corresponding to the etching selective ratio in the case of 100 MHz is
larger than the value corresponding to the etching selective ratio in the
case of 40 MHz. That is, from the experimental result of the samples for
estimation, it was confirmed that the possibility of etching the
organic-material film with a high etching rate and a high etching
selective ratio is higher in the case of 100 MHz than in the case of 40
MHz. The power of the high-frequency electric power of 100 MHz is
preferably in a range of about 1.0 W/cm2 to about 5.0 W/cm2,
because the etching rate and the etching selective ratio of the
organic-material film are in a tradeoff relationship.

[0111]Next, regarding the wafer W having the structure (real pattern)
shown in FIG. 9A, while the resist film 45 and the inorganic-material
film 43 consisting of SiO2 were used as a mask, the organic-material
film 42 consisting of a low-k film was etched by the unit shown in FIG. 1
by using the high-frequency electric power of 40 MHz and 100 MHz,
respectively. The etching condition of this case was the same as that in
the above etching experiment of the whole-surface formed films. Herein,
as the organic-material film 42, SiLK (commercial name) being a low-k
film and made by DowChemical company was used. A thickness thereof was
570 nm, a thickness of the SiO2 film 43 thereon was 200 nm, a
thickness of the BARC film 44 thereon was 60 nm, and a thickness of the
resist film 45 was 800 nm. The etching process was continued for a time
that is 1.5 times as long as that until the organic-material film 42 is
completely etched (50% over etching). The time for which the SiO2
film is exposed to the plasma was lengthened. That is, the condition was
severe on the SiO2 film.

[0112]The result is shown in FIGS. 17 and 18. FIG. 17 is a graph showing
relationships between a high-frequency electric power and an etching rate
of the organic-material film and relationships between a high-frequency
electric power and a shoulder loss of the inorganic-material film. FIG.
18 is a graph showing relationships between an etching rate of the
organic-material film and an etching selective ratio with respect to an
etching rate of a shoulder part of the inorganic-material film, in
respective cases wherein the frequency of the high-frequency electric
power is 40 MHz or 100 MHz. Herein, the shoulder loss means an etched
volume of the shoulder part. Specifically, as shown in FIG. 19, the
shoulder loss means a height distance (shown by Y in the drawing) from
the original surface of the inorganic-material film 43 to an etched
(deepest) position of the shoulder part. In addition, the etching
selective ratio at the shoulder part in FIG. 18 means a ratio of the
etching rate of the organic-material film with respect to the etching
rate at the shoulder part of the inorganic-material film 43 calculated
from the value of the shoulder loss.

[0113]As shown in FIG. 17, in the respective high-frequency electric
powers, when the respective results in the cases of 100 MHz and 40 MHz
are compared with each other, the shoulder loss is at the same level, but
the etching rate of the organic-material film is higher in the case of
100 MHz. In addition, as shown in FIG. 18, in the real pattern, in the
same manner as FIG. 16 showing the results of the samples for estimation,
when the etching selective ratio is the same, the etching rate of the
organic-material film is higher in the case of 100 MHz. When the etching
rate is the same, the etching selective ratio tends to be higher in the
case of 100 MHz. That is, in the etching process of the real pattern, it
was confirmed that the organic-material film can be etched with a high
etching rate and a high etching selective ratio when the high-frequency
electric power of 100 MHz, other than 40 MHz, is used.

[0114]In the above experiment, the gap between the electrodes was 27 mm.
As described above, if the distance between the electrodes is too small,
pressure distribution (pressure difference between at a central portion
and at a peripheral portion) on the surface of the wafer W, which is a
substrate to be processed, becomes so large that deterioration of the
etching uniformity or the like may be generated. Thus, in practice, the
distance between the electrodes is preferably 35 to 50 mm. This is
explained with reference to FIG. 20.

[0115]FIG. 20 is a graph comparatively showing relationships between an
Ar-gas flow rate and a pressure difference ΔP of a central portion
of the wafer and a peripheral portion thereof, in respective cases
wherein the electrode gap is 25 mm or 40 mm, wherein the Ar gas is used
as a plasma gas. As shown in FIG. 20, the pressure difference ΔP is
smaller when the gap is 40 mm rather than 25 mm. In addition, in the case
of the gap of 25 mm, when the Ar-gas flow rate is increased, the pressure
difference ΔP tends to be sharply increased. When the gas flow rate
is higher than about 0.3 L/min, it exceeds 0.27 Pa (2 mTorr) as an
allowable maximum pressure difference ΔP, at which deterioration of
the etching uniformity or the like may not be generated. On the other
hand, in the case of the gap of 40 mm, independently on the gas flow
rate, the pressure difference is smaller than 0.27 Pa (2 mTorr). Thus, it
can be expected that the allowable maximum pressure difference ΔP
at which deterioration of the etching uniformity or the like may not be
generated is ensured, independently on the gas flow rate, if the
electrode gap is not less than about 35 mm.

[0116]Next, regarding a 300 mm wafer having the real pattern shown in FIG.
9A, respective films having the same thicknesses as the example shown in
FIGS. 17 and 18, while the resist film 45 and the inorganic-material film
43 consisting of SiO2 were used as a mask, the organic-material film
42 consisting of a low-k film was etched. Herein, according to the manner
shown in FIG. 10, two high-frequency electric power sources of 100 MHz
and 3.2 MHz were connected to the supporting table 2, the high-frequency
electric power of 100 MHz was fixed to 2400 W, and the second
high-frequency electric power of 3.2 MHz was changed between 0 W, 200 W,
800 W, 1600 W and 3000 W. As the process gas, an N2 gas and an
H2 gas were used. The pressure in the chamber was changed between
13.3 Pa (100 mTorr), 31.7 Pa (450 mTorr) and 106.7 Pa (800 mTorr). The
flow rate of the process gas was the N2 gas: 0.5 L/min and the
H2 gas: 0.5 L/min in the case of 13.3 Pa, and the N2 gas: 0.65
L/min and the H2 gas: 0.65 L/min in the cases of 31.7 Pa and 106.7
Pa. The electrode gap was 40 mm. The etching process was conducted as 50%
over etching in the same manner as the above example.

[0117]The result is shown in FIGS. 21 to 23. FIG. 21 is a graph showing
relationships between the power of the second high-frequency electric
power of 3.2 MHz and an etching rate of the organic-material film and
relationships between the power of the second high-frequency electric
power of 3.2 MHz and an etching selective ratio with respect to the
shoulder part, in respective pressure conditions. FIG. 22 is a graph
showing relationships between the power of the second high-frequency
electric power of 3.2 MHz and a top CD shift, in respective pressure
conditions. FIG. 23 is a graph showing relationships between the power of
the second high-frequency electric power of 3.2 MHz and a bowing value,
in respective pressure conditions. Herein, as shown in FIG. 24, the top
CD shift means a value showing how much a top CD is changed through the
etching process, the top CD meaning an etching opening at an upper-end
portion of the organic-material film 42. That is, the top CD shift means
a value obtained by subtracting an original top CD (TopCDbf) from a top
CD after the etching process (TopCDaf). In addition, the bowing value
means a value obtained by subtracting the top CD (TopCD) from a maximum
width (MaxCD) at an etched portion after the etching process of the
organic-material film.

[0118]In the example, since the pressure in the chamber is 13.3 Pa or
higher, ion dispersion is great, so that vertical component of ion energy
is relatively reduced. Thus, as shown in FIG. 21, when the power of the
second high-frequency electric power (bias power) of 3.2 MHz is
relatively low, the inorganic-material mask is hardly etched. That is,
the organic-material film can be etched with a high etching selective
ratio with respect to the inorganic-material mask. Furthermore, in the
case, the etching rate of the organic-material film is also high. In
addition, at the same bias power, the etching selective ratio tends to be
higher under a condition of a higher pressure wherein the vertical
component of ion energy is less. In addition, in each pressure, when the
power of the second high-frequency electric power of 3.2 MHz is
increased, the etching rate of the organic-material film is increased
while the etching selective ratio at the shoulder portion tends to be
lowered. If the power of the second high-frequency electric power of 3.2
MHz is low, an ion-drawing force to the wafer is weak so that ions are
supplied to the inorganic-material mask only very softly. Thus, the
inorganic-material mask is hardly etched, so that a high etching
selective ratio can be obtained. On the other hand, when the power of the
second high-frequency electric power of 3.2 MHz is increased, the
ion-drawing force to the wafer becomes stronger, so that the etching rate
of the organic-material film is increased but the etching rate of the
inorganic-material film is also increased. Thus, the etching selective
ratio is deteriorated. In the case of the pressure of 13.3 Pa, when the
bias power is 1600 W (power density: 2.26 W/cm2) that is high, the
etching rate of the organic-material film is 400 nm/min that is high, but
the etching selective ratio is reduced to about 3 or 4. This feature is
usable for some applications. However, it can be expected that a bias
power higher than the above is not usable because the etching loss of the
inorganic-material mask is too much. In the case of the pressure of 106.7
Pa, even when the bias power is 3000 W (power density: 4.25 W/cm2),
the etching selective ratio is maintained at about 5. This feature is
usable for some applications. Then, the etching rate of the
organic-material film is 550 nm/min, which is very high. However, even in
the case of the pressure of 106.7 Pa, it is expected that a bias power
higher than 3000 W (power density: 4.25 W/cm2) is not usable because
the etching loss of the inorganic-material mask is too much.

[0119]As shown in FIG. 22, the top CD shift tends to be better in the case
of the pressure of 13.3 Pa than in the case of the pressure of 106.7 Pa.
Furthermore, in the case of 13.3 Pa, when the bias power is increased,
the top CD shift is reduced, and when the bias power is 1600 W (power
density: 2.26 W/cm2), the top CD shift is about 2 to 3 nm. In the
case of the pressure of 106.7 Pa, independently on the bias power, the
top CD shift is 30 nm. In the case of the pressure of 106.7 Pa, the top
CD shift is near to the upper limit of an allowable range. Thus, the
substantially upper limit of the pressure in the chamber is 106.7 Pa.

[0120]As shown in FIG. 23, the bowing value tends to be lower in the case
of the pressure of 106.7 Pa than in the case of the pressure of 13.3 Pa,
at the same bias power. In addition, in the case of 106.7 Pa, when the
bias power is increased, the bowing value is increased, and when the bias
power is 3000 W (power density: 4.25 W/cm2), the bowing value is 30
nm. When the bias power is higher than 3000 W, it is expected that the
bowing value exceeds 30 nm. Thus, the upper limit of the bias power is
3000 W (power density: 4.25 W/cm2).

[0121]Next, regarding a 300 mm wafer having the real pattern shown in FIG.
9A, respective films having the same thicknesses as the example shown in
FIGS. 17 and 18, while the resist film 45 and the inorganic-material film
43 consisting of SiO2 were used as a mask, the organic-material film
42 consisting of a low-k film was etched. Herein, according to the manner
shown in FIG. 10, two high-frequency electric power sources of 100 MHz
and 3.2 MHz were connected to the supporting table 2, the high-frequency
electric power of 100 MHz was fixed to 2400 W, and the second
high-frequency electric power of 3.2 MHz was changed between 0 W, 200 W
and 400 W. As the process gas, an N2 gas and an H2 gas were
used. The pressure in the chamber was changed between 1.33 Pa (10 mTorr),
3.99 Pa (30 mTorr), 6.65 Pa (50 mTorr) and 13.3 Pa (100 mTorr). The flow
rate of the process gas was the N2 gas: 0.12 L/min and the H2
gas: 0.12 L/min in the case of 1.33 Pa, the N2 gas: 0.18 L/min and
the H2 gas: 0.18 L/min in the cases of 3.99 Pa, the N2 gas: 0.3
L/min and the H2 gas: 0.3 L/min in the cases of 6.65 Pa and the
N2 gas: 0.5 L/min and the H2 gas: 0.5 L/min in the cases of
13.3 Pa. The electrode gap was 40 mm. The etching process was conducted
as 50% over etching in the same manner as the above examples.

[0122]For each sample after the etching process, an etching residue, a
shoulder loss of the inorganic-material film (mask) and a top CD shift
were obtained. The result is shown in FIGS. 26 and 27. FIG. 26 is a graph
showing etching residues, shoulder losses of the inorganic-material film
(mask) and top CD shifts, in respective pressure conditions, when the
bias power (of the second high-frequency electric power source) is zero.
FIG. 27 is a graph showing shoulder losses of the inorganic-material film
(mask), top CD shifts and etching rates of the organic-material film, in
respective bias-power conditions, when the pressure is 3.99 Pa.

[0123]As shown in FIG. 26, no etching reside was generated when the
pressure was 6.65 Pa or lower, but some etching reside was generated when
the pressure was 13.3 Pa. The shoulder loss of the inorganic-material
film was 0 in the cases of 3.99 Pa, 6.65 Pa and 13.3 Pa. The shoulder
loss of the inorganic-material film was 42 nm in the case of 1.33 Pa,
which value is relatively large but within an allowable range. The top CD
shift was -3 nm in the case of 3.99 Pa, and +5 nm in the case of 6.65 Pa,
which values are very small. In addition, it was confirmed that the
absolute value of the top CD shift is increased both when the pressure is
higher than 6.65 Pa and when the pressure is lower than 3.99 Pa. The top
CD shift was -30 nm in the case of 1.33 Pa, which value is approximately
within an allowable range. From these results, it was confirmed that the
pressure is preferably within a range of 1.33 to 6.65 Pa in order to
conduct an etching process wherein the shoulder loss is small (that is,
the etching selective ratio is high), the etching residue is less, and
the top CD shift is small.

[0124]In addition, as shown in FIG. 27, when the bias power is increased,
the shoulder loss tends to be increased and the absolute value of the top
CD shift tends to be increased. However, when the bias power is 400 W
(power density: 0.566 W/cm2) or lower, the respective values of the
shoulder loss and the top CD shift were within usable ranges. It is
estimated that the shoulder loss becomes too large when the bias power
exceeds 400 W. In addition, the etching rate tends to be increased when
the bias power is increased.

[0125]From the above results, it was confirmed that: in order to enhance
the etching selective ratio, to reduce the top CD shift, and to prevent
generation of the etching residue, it is sufficient that the pressure in
the chamber is 1.33 Pa to 6.65 Pa and the bias power density is not
higher than 0.566 W/cm2.

[0126]The present invention is not limited to the above embodiment, but
may be variously modified. For example, in the above embodiment, as the
magnetic-field generating means, the annular magnetic unit in the
multi-pole state is used wherein the plurality of segment magnets
consisting of permanent magnets are arranged annularly around the
chamber. However, the present invention is not limited to this manner if
a magnetic-field can be formed around the processing space to confine the
plasma. In addition, the peripheral magnetic field for confining the
plasma may be unnecessary. That is, the etching process can be conducted
under a condition wherein there is no magnetic field. In addition, the
present invention can be applied to a plasma etching process conducted in
a crossed electromagnetic field wherein a horizontal magnetic field is
applied to the processing space. In addition, in the above embodiment,
the high-frequency electric power for generating plasma is applied to the
lower electrode, but may be applied to the upper electrode. In the above
embodiment, the low-k film is used as the organic-material film, but
other films including O, C and H or other films including Si, O, C and H
may be also used. In addition, the semiconductor wafer is taken as an
example of the substrate to be processed. However, this invention is not
limited thereto, but applicable to other plasma processes for an LCD
substrate or the like. In addition, the above description is about the
case wherein the organic-material film is etched by using the
inorganic-material film as a mask, but this invention is not limited
thereto. This invention is applicable to all cases to selectively etch an
organic-material film with respect to an inorganic-material film. For
example, this invention is applicable to an ashing process to remove a
resist that has been used as a mask when an inorganic-material film, for
example a SiO2 film, formed on a substrate to be processed, for
example a Si wafer or the like, is etched. The ashing process has to be
conducted so as to selectively and efficiently remove the resist film
being an organic-material film, with etching the inorganic-material film
under the resist film as little as possible. Thus, if the present
invention is applied to the ashing process, a good ashing characteristic
can be achieved.